泥盆系弗拉阶/法门阶之交事件沉积和海平面变化

在华南板块南部被动大陆边缘和西伯利亚板块南部活动大陆边缘弗拉阶/法门阶之交识别出7种物理事件相: 细粒钙屑浊积岩相、钙质角砾岩相、软变形灰岩相、含微球粒的粒泥灰岩相、凝灰质砾岩相、黑色页岩相和火山喷溢相.它们在法门阶下Palmatolepis triangularis带底部和/或上Palmatolepis rhenana带底部具有广泛的分布, 可能是两次陨击事件记录, 是良好的高分辨率年代地层对比标志.弗拉期/法门期之交的海平面变化不具有同步性和一致性, 可分辨出2种型式(阶跃型和渐进型) 和5种状态(弗拉期最末期下降→法门期最初期上升、弗拉期最末期上升→法门期最初期下降、弗拉期最末期上升→法门期最初期上升、弗拉期最末期下降→法门期最初期下降、弗拉期最末期与法门期最初期海平面变化不明显).弗拉阶/法门阶之交生物的阶梯状绝灭可能与从上Palmatolepis rhenana带底部至Palmatolepis crepida带不均匀分布的6次陨击事件密切相关. 

DEVONIAN FRASNIAN/FAMENNIAN TRANSITIONAL EVENT DEPOSITS AND SEA-LEVEL CHANGES

Seven kinds of physical event deposits have been recognized in the Frasnian/Famennian transition of both the passive continental margin of the South China plate and southern active continental margin of the Siberian plate. They are fine calcareous turbidite facies, calcareous breccia facies, limestone facies with soft-sediment deformation, wackestone facies with microspherules, tuffaceous breccia facies, black shale facies and volcanic explosive and effusive facies and they are widely distributed in the bottom of the Lower Palmatolepis triangularis zone of the Famennian and/or in the bottom of the Upper Palmatolepis rhenana zone of the Frasnian. These event deposits must have been induced by two-time asteroid impact events and should be good indicators of high resolution chronostratigraphic correlation. Data indicated that the sea-level changes were not synchronal and that there existed two types of saltatory and gradual sea level changes, and five kinds of different characteristics in sea-level changes from the latest Frasnian to the earliest Famennian in China and other regions of the world. They were the latest Frasnian sea-level falling → the earliest Famennian sea-level rising, the latest Frasnian sea-level rising → the earliest Famennian sea-level falling, the latest Frasnian sea-level rising → the earliest Famennian sea level rising, the latest Frasnian sea-level falling → the earliest Famennian sea-level falling, the Frasnian/Famennian transitional sea-level still. The stepped mass extinction of the Frasnian/Famennian transition may be closely related to six-time asteroid impact events from the bottom of the Upper Palmatolepis rhenana zone to the Palmatolepis crepida zone.